Cross-species comparison of human and rodent primary reward consumption under budget constraints

Abstract

Optimal use of resources is of great importance for survival of all species. Previous studies have shown that rats optimize their allocation of a limited number of operant responses (akin to a finite budget) to trade for food rewards. Here, we propose a novel human cost-benefit decision paradigm translated from an economic task initially developed for rodents, to conduct a cross-species comparison of primary reward consumption under budget constraints. Participants had a limited budget of effortful button-presses to obtain the opportunity to drink milk rewards or watch erotic pictures. Like rodents, they adapted their choice allocation when the price (i.e. fixed-ratio requirement for reward) and the budget changed when purchasing milk rewards. However, this was not the case when purchasing the opportunity to watch erotic pictures: compared to the milk and to the rodent task, participants made more internally inconsistent, hence, irrational choices, despite otherwise identical task structures. We found non-linear changes in arousal as a function of reward selection that might underlie the irrationality in the picture task. Our study shows that the type of reward matters not only for capturing the convergence in human and non-human economic decision-making, but also for understanding the factors behind compromised economic rationality.